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| author | H. Peter Anvin <hpa@linux.intel.com> | 2010-05-17 15:13:23 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@linux.intel.com> | 2010-05-17 15:17:16 -0700 |
| commit | c59bd5688299cddb71183e156e7a3c1409b90df2 (patch) | |
| tree | d7b99407367b30aa7766219083ad0262c8edbab8 /arch/x86/include/asm/alternative.h | |
| parent | 4677d4a53e0d565742277e8913e91c821453e63e (diff) | |
| download | blackbird-op-linux-c59bd5688299cddb71183e156e7a3c1409b90df2.tar.gz blackbird-op-linux-c59bd5688299cddb71183e156e7a3c1409b90df2.zip | |
x86, hweight: Use a 32-bit popcnt for __arch_hweight32()
Use a 32-bit popcnt instruction for __arch_hweight32(), even on
x86-64. Even though the input register will *usually* be
zero-extended due to the standard operation of the hardware, it isn't
necessarily so if the input value was the result of truncating a
64-bit operation.
Note: the POPCNT32 variant used on x86-64 has a technically
unnecessary REX prefix to make it five bytes long, the same as a CALL
instruction, therefore avoiding an unnecessary NOP.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Borislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <alpine.LFD.2.00.1005171443060.4195@i5.linux-foundation.org>
Diffstat (limited to 'arch/x86/include/asm/alternative.h')
0 files changed, 0 insertions, 0 deletions
